XS400 Member
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Minnesota, USA
I recently have started working on my uncle's/dad's XS400, my first motorcycle project. I have worked with QT50's and other small mopeds in the past, but nothing this size. The bike hasn't been ridden seriously since the '90s as far as I know, although it has ran a few times since then.

Today I cleaned/rebuilt the carbs, I am currently waiting on new OEM style airboxes so I can start trying to get things tuned and balanced. I used 142.5 main jets, I believe that this is the factory size, correct me if I am wrong. I also set my floats to just over 31mm, measured with a caliper to the top of the float while they are resting on the needles. I am unsure of where to start the mix screws at, I currently have them set about 2.5 turns out from being bottomed out.

After I put the carbs back on, I filled the bowls and tried to start the bike. I got it to fire and run briefly before my fuel ran out.

Tonight, I attempted to tackle the clutch. The cable was lengthen with an extra piece and the clutch was very fast while riding. I removed the rear clutch cover on the left hand side of the bike. It was packed with mud so I used degreaser and a wire brush to clean it up.

Next I did something that may have been a mistake in hindsight. I removed the main engine cover on the left side in attempt to clean up the years of mud. The gasket appears to be holding up alright, but I was wondering if a replacement would be available, should I need one. I took the smaller outer cover off and removed the allen bolts from the stator inside. I called it quits after this because I could not figure out how to get the cover off the unit. A coil seems to be coming off with the cover, but the wires running out of the cover seem to be holding me up.

Further, I am hoping to inspect the starter while I have this left side apart. I suspect it may be wearing out, or it's gears because it will occasionally make a bad sounding clunk/grinding noise when cranking the bike. Is the left side the correct side for starter inspection, or is that on the right. Either way, I will likely take the right side off as well to clean up the mud and crud over there too.

I've attached some pictures of the bike and my current clutch/starter/cleanup project. Hopefully they will work.
IMG_0110[1].JPG IMG_E0107[1].JPG IMG_E0108[1].JPG IMG_E0109[1].JPG

Any advice or recommendations is always welcome. Thanks!
I have answered my own question about taking off the left cover with a great post from Drewcifer.

I should be able to follow the wires through the muddy mess underneath and find the connector and disconnect and remove the copper coil, along with the wires that seemed to be impeding my ability to remove the cover.
Welcome to the forum. Your bike looks to be a 81-H model bike. Your main jets should be 135 and the floats should be set at 26mm (for brass ones). Pilot mix screws should be around 3 turns out for a stock intake and muffler bike. I would set your valves and then sync the carbs with a manometer. The three bolts that hold your field coil on don't need to be removed in order to pull the cover off. In fact you could damage it. I few taps with a rubber mallet should loosen the cover. Be very careful with those wires.
Thanks Chris. I will take a look at those floats again today. I was using the "Haynes XS400" service manual and set the floats and jets according to that. I noticed that the supplemental manual for the "XS 400 H, SH" had some discrepancies so I will use that on going forward. Thanks for the heads up.

According to the Yamaha Service Manual, intake valve gap should be .1mm or .0039 inches, and the exhaust should be .18mm or .0071 inches. Is this correct?
I use .004 and .007 for valves. Make sure to adjust from left to right and only turn the motor in the one direction indicated on the crank come to reach TDC. DON'T turn the motor "back" to catch the mark if you miss it as this will put slack in the timing chain giving you a bad adjustment. There are threads on this in the forum. As for the float height the manual has 32mm for fuel level. It's another way to check float height but with gas in the bowl and carbs on the bike. I have never needed to do this and have had very good results with just setting the float height. Make sure to set it without the gasket on the carb and check both sides of the float.
I got the valves set and finished cleaning things up down by the clutch.

I replaced the old fuse box with a homemade 3D printed one and it seems to be working well. While I was working with the electronics I removed the harness and cleaned things up and re-taped some sections. After I got everything reinstalled, everything appears to be working except for spark. I have 12v at both ignition coils when the key is turned. I am beginning to worry that I might have gotten the TCI wet.

I have tested the pickup coil and gotten a reading around 700 ohms, which aligns with the manual, I also tested the primary coil on both ignition coils and got around 3.3 ohms (that is between orange and red/white and between grey and red/white). I think the procedure for testing the secondary is to test from one of the two primary wires and the spark plug boot. When I do this, I get no continuity, which suggests bad coils, but I had spark on both coils prior to the electrical project and simultaneous failure seems unlikely.

What further testing should I try?

Thanks in advance for your help!

EDIT: I was able to test the secondaries and they seem to be within spec. Should I assume a bad TCI now?
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Turns out the White-Green wire going to the plug was compromised and I replaced it with a blade style plug and it seems to be working. Might replace the plug at some point if I can find one.